Damping valve for power steering

ABSTRACT

In a damping valve for pressure medium-actuated operating circuits, a spring element is installed between housing, cover and counter-contour. In the opening direction, the spring element is pressed against the counter-contour by the pressure medium flowing through, so that a flow passage cross-section allowing almost unimpeded passage of the pressure medium is obtained. In the opposite direction, the throttling direction, the spring element rests on the cover and blocks the flow of the pressure medium until a well-defined pressure builds up, which lifts the inner side of the spring element from the counter-contour and thus opens a reduced flow passage cross-section.

FIELD OF THE INVENTION

The present invention relates to a damping valve for pressuremedium-actuated operating circuits and to the use of such a dampingvalve in a power steering system for motor vehicles. In the dampingvalve, a flow passage cross-section is regulated by the interaction ofhousing, spring element, cover, and counter-contour.

BACKGROUND INFORMATION

In hydraulically or pneumatically actuated operating circuits,vibrations may arise which originate, for example, in the servo pump ordue to impacts from a user. In power steering systems such vibrationscan be generated, for example, by shocks introduced by the roadway intothe steered wheels of the vehicle or into the power steering system.

French Published Patent Application No. 2 632 371 describes a dampingvalve which separates two pressure chambers from one another andinfluences the volume flow path between the two pressure chambers in acontrolled manner. The damping valve has an elastic valve plate which isnormally in a neutral position and, when a pressure difference arisesbetween the two chambers, is displaced from its neutral position towardthe lower pressure. A disadvantage of these damping valves is the largenumber of component parts and the associated large space required forinstallation. Another disadvantage is the fact that these nonreturnvalves operate in only one direction and the damping characteristics ofthese valves can be influenced only to a very limited extent. FrenchPublished Patent Application No. 1 535 025 describes a damping valve forpressure medium actuated circuits having a housing and a flow-throughchannel between two pressure medium connections. German Published PatentApplication No. 196 03 183 describes a power steering system for a motorvehicle in which damping valves are arranged in the operating linesbetween a control valve and the working chambers of a servo motor.

It is therefore an object of the present invention to provide a dampingvalve having a simple design which is versatile in its application,operates in both directions and can exhibit different dampingcharacteristics.

The above and other beneficial objects of the present invention areachieved by providing a damping valve in which a spring element isexposed to pressure or by the flow of a medium, whereby a variablecross-sectional area can be obtained which produces the desired dampingeffect through variable throttle geometries, depending on theconfiguration. The same or different damping characteristics may beachieved in the two directions of flow.

The damping valve can be represented very simply by the interaction of aspring element and a counter-contour. The spring element is designedpreferably in the form of a circular disk which can be displaced axiallywithin a housing. Further variants include spring elements in the formof polygons or curves. The characteristics of the damping valve can bemodified by variations in the spring element, the cross-section, and thecounter-contour.

In order to modify the flow passage cross-section, the outer and/orinner contour of the spring element is designed so that it can moveaxially in relation to the contour of the housing. Along its axialextension, the contour of the housing has different cross-sections,through which the damping characteristics can be influenced.

The mobility of the outer and/or inner contour of the spring element canbe achieved due to the fact that the spring element is centrallysupported on the housing or on the counter-contour, and is made of anelastic material. The movable contour of such a spring element can beadjusted in an axial direction as a function of the pressure and flowconditions in the damping valve.

A damping action can be produced even for the smallest movements bypre-stressing the spring element in a controlled manner. This allowspressure to be controlled even in the case of a flat counter-contour, bythe axial positioning of the spring element and variable openingcross-sections.

By specifying a free opening, for example through a bent spring element,a permanent flow can also be implemented, which allows the dampingaction to begin only at higher flow rates.

In the case of power steering systems of motor vehicles, undesirablevibration and noise effects, for example, can thus be suppressed.

In its simplest form, the damping valve may be manufactured as a compactunit having three parts, forming the basis for adjustable damping valveshaving a wide range of damping characteristics.

The free choice of housing, counter-contour and spring element evenpermits the creation of damping functions, i.e., the dampingcharacteristics can be varied as a function of different parameters.

If a flow passage cross-section of the damping valve at its neutralsetting is selected that is large enough to allow unimpeded passage upto a certain volume flow rate, the overall size of the damping valve canbe kept small. In addition, this permits a design which is particularlyinsensitive to the flow rate, and thus also insensitive to noise.

There are many ways of configuring the characteristics of the dampingvalve. For instance, the pressure level can be raised or lowered usingthe adjusting screw. The increase of the slope of the pressure/volumeflow curve can be modified by selection of the fit between dampingelement and housing.

The timing of the beginning of the damping effect can be influenced byvarying the rigidity of the damping element, e.g., through the selectionof the thickness of the damping element.

The use of such damping valves in power steering systems of motorvehicles is particularly advantageous, since in this case a very limitedinstallation space is available and different types of vibration canoccur, with noise effects and negative effects on the steering responsewhich can be individually eliminated through the variability of thedamping valve.

FIG. 1 is a partial longitudinal cross-sectional view of a powersteering system that may be equipped with a damping valve according tothe present invention.

FIG. 2 illustrates an example embodiment of a damping valve according tothe present invention.

FIG. 3 illustrates another example embodiment of a damping valveaccording to the present invention.

FIG. 4 illustrates another example embodiment of a damping valveaccording to the present invention.

FIG. 5 illustrates another example embodiment of a damping valveaccording to the present invention.

FIG. 6 illustrates another example embodiment of a damping valveaccording to the present invention.

FIG. 7 illustrates another example embodiment of a damping valveaccording to the present invention.

FIG. 8 illustrates an example embodiment of an adjustable damping valveaccording to the present invention.

FIG. 9 illustrates an example embodiment of a damping valve having anadditional switching element according to the present invention.

FIG. 10 illustrates another example embodiment of a damping valveaccording to the present invention.

FIG. 11 illustrates another example embodiment of a damping valveaccording to the present invention.

FIG. 12 illustrates an application of an example embodiment of a dampingvalve according to the present invention.

FIG. 13 illustrates another example embodiment of a damping valveaccording to the present invention.

DETAILED DESCRIPTION

A rack and pinion power steering system is described as one example ofthe application of the damping valves according to the presentinvention. The damping valves according to the present invention may,however, be used in any hydraulically or pneumatically supportedoperating circuit.

A drive pinion 2 is rotatably mounted on two bearings 3 and 4 in asteering housing 1. A steering shaft connection 5 is located at one endof drive pinion 2.

The teeth of drive pinion 2 engage with a rack 6 which is axiallydisplaceable within the steering housing.

A servo motor with a piston rod 8 having a fixed connection to rack 6may be used for servo support. Servo motor 7 has two working chambers 11and 12 in a cylinder 10. These working chambers are separated from oneanother by piston 13 which is firmly fixed to piston rod 8. Workingchambers 11 and 12 are connected via operating lines 14 and 15 to twocylinder connections 16 and 17 of a control valve 18. In addition,control valve 18 has an inlet connection 20 to which a pressure source21 in the form of a servo pump is connected. A container 23 is connectedto a return connection 22. Operating lines 14 and 15 are connected tocylinder 10 via two connecting pieces 24 and 25.

A damping valve 26 is arranged in each of the two operating lines 14 and15 between control valve 18 and working chambers 11 and 12 of servomotor 7. Damping valves 26 may be arranged either in cylinderconnections 16 and 17 on control valve 18, or in connecting pieces 24and 25 on cylinder 10 of servo motor 7, or directly in operating lines14 and 15.

Damping valve 26 is shown in FIG. 2 in the first exemplary embodiment.

A spring element 27 is installed between housing 28, cover 29, andcounter-contour 30. In the opening direction, spring element 27 ispressed toward counter-contour 30 by the pressure medium passingthrough, so that a flow passage cross-section is obtained which allowsalmost unimpeded passage of the pressure medium. In the oppositedirection, the throttling direction, spring element 27 rests on cover 29and initially blocks the flow of the pressure medium until a certainpressure has built up which lifts the inner side of spring element 27from counter-contour 30, thus opening a reduced flow passagecross-section. Thus, in the damping direction, by the adjustment ofspring element 27 and counter-contour 30 with respect to one another, aprecisely defined damping pressure of damping valve 26 may be set. Thecurve characteristics that can be achieved using this variant show a lowdegree of damping in the opening direction and a high degree of dampingwith a function having a sharply increasing slope in the throttlingdirection.

The damping effect of damping valve 26 may also be influenced throughthe geometry of spring element 27 itself. In FIG. 3, for example,damping is achieved using a pre-bent spring element 27, which in theneutral position is not tightly closed on the outer periphery, but is inpart slightly open. Thus no throttling takes place under conditions ofslow, quasi-static flow. However, in the case of dynamic flow in thethrottling direction, spring element 27 initially rests on its entireperiphery, thus closing the flow passage cross-section. At a certainpressure level, the spring element opens on the inner side, thusallowing a damped flow of the pressure medium. The corresponding curvelikewise shows a limited damping effect in the open direction, while thecharacteristics in the damping direction are variable. Thus, underconditions of slow flow, a slow increase in pressure occurs, whereasunder conditions of fast flow, there is an abrupt increase in pressureas a function of the flow rate. Shocks and vibrations introduced by thevehicle wheels, for example, may be reduced by a sharp increase inpressure, while unpleasant sluggishness in the steering can be avoidedby a slow increase in pressure with even flow rates and steering speeds.

As shown in FIG. 4, the curve characteristics may be influenced by anadditional bore hole 31 in counter-contour 30, so that in the dampingdirection a parabolic increase in the slope of the pressure/flow ratecurve may be obtained.

By integrating an additional valve 33 into damping valve 26, a blockingeffect may be achieved, up to a certain volume flow rate, leading to anabrupt increase in the slope of the pressure/flow rate curve.

If a labyrinth system 34 as illustrated in FIG. 6 is used instead ofvalve 33 shown in FIG. 5, dynamic effects caused by shocks introduced bythe roadway can be largely throttled by the associated turbulence.

In order to adapt the damping valve according to the present inventionto any type of vehicle in an optimum manner, damping valve 26 may alsobe designed in an adjustable or switchable version. FIG. 7 shows such anembodiment. Counter-contour 30 is designed as an adjusting screw 32,which allows the pressure level of the characteristic curve of dampingvalve 26 to be influenced. Spring element 27 may be pre-stressed usingadjusting screw 32, allowing the parameters determining the beginning ofthe damping effect to be influenced. A flow rate-dependent dampingresponse can thus be obtained using adjusting screw 32.

FIG. 8 shows an adjustable damping valve having an additional bore holein the adjusting screw, which allows a smoother increase in the slope ofthe characteristic curve to be achieved.

FIG. 9 shows an example embodiment having an additional switchingelement 36 designed to be movable on an extension 35. In the returndirection, switching element 36 is pressed away from spring element 27,thus opening a gap for unimpeded flow. In contrast, in the throttlingdirection, switching element 36 is initially pushed up to a stop 37 onextension 35 and only then does it engage spring element 27 to controlthe variation in pressure.

In the throttling direction, a specified basic flow rate which changeswith increasing volume flow rate can be set by a variable geometry 38 ofadjusting screw 32, as shown in FIG. 10. The pressure/flow ratecharacteristics can be set as desired by varying the contour of theadjusting screw.

Another example embodiment of the present invention is shown in FIG. 11.Adjusting screw 32, having an outer side used for guiding spring element27, is provided with recesses 39 for the passage of flow. Spring element27 is supported in its axial movement only at two points on cover 29, sothat in the throttling direction, due to the lever effect, the pressuremedium can flow past not only on the inner side of the spring elementbut also on the outer side.

FIG. 12 shows an application of damping valve 26 according to thepresent invention. Damping valve 26 may be retrofitted into an operatingline 14 using two adapters 40 and 41.

FIG. 13 shows another example embodiment of damping valve 26 accordingto the present invention. This is a damping valve cartridge 43 which hasa hollow screw 42, a spring element 27 and a counter-contour 30. Theinner contour of hollow screw 46 performs the function of housing 28 andcover 29. This damping valve cartridge 43 may be easily retrofitted intomotor vehicle steering systems.

The spring element 27 may include at least one throttle bore hole 45.

What is claimed is:
 1. A damping valve for a pressure medium actuatedoperating circuit of a steering system for a motor vehicle, comprising:a housing; a first flow-through channel disposed between two pressuremedium connections; a counter-contour; and a flat spring elementconfigured to vary a cross-section of the first flow-through channel;wherein the spring element includes at least one central bore hole, afirst one of an inner contour and an outer contour of the spring elementaxially movable inwardly in accordance with a first direction of flow, asecond one of the inner contour and the outer contour of the springelement axially movable outwardly in accordance with a second directionof flow opposite the first direction of flow, the counter-contourincluding at least one bypass bore hole configured to permit thepressure medium to bypass the spring element, the at least one bypassbore hole providing a second flow-through channel between the twopressure medium connections.
 2. The damping valve according to claim 1,wherein the flow-through channel cross-section is variable as a functionof pressure and flow rate.
 3. The damping valve according to claim 1,wherein the spring element is axially displaceable.
 4. The damping valveaccording to claim 1, wherein the housing includes at least onethrottling point.
 5. The damping valve according to claim 1, furthercomprising an adjusting screw integrated in the housing.
 6. The dampingvalve according to claim 5, wherein at least one throttling point isprovided in the adjusting screw.
 7. A damping valve for a pressuremedium actuated operating circuit of a steering system for a motorvehicle, comprising: a housing; a flow-through channel disposed betweentwo pressure medium connections; a counter-contour; and a flat springelement configured to vary a cross-section of the flow-through channel;an additional switching element movably arranged on an extension;wherein the spring element includes at least one central bore hole, thespring element axially movable inwardly and outwardly in accordance witha direction of flow, the switching element acting inwardly and outwardlyin accordance with the direction of the flow, the counter-contourincluding at least one bore hole configured to permit the pressuremedium to bypass the spring element.
 8. The damping valve according toclaim 5, wherein the adjusting screw includes a curve-shaped outercontour.
 9. The damping valve according to claim 5, wherein theadjusting screw includes at least one recess arranged for the passage ofa flow volume.
 10. The damping valve according to claim 1, wherein thespring element includes at least one throttle bore hole.
 11. A method ofusing a damping valve for a pressure medium actuated operating circuitof a steering system for a motor vehicle, the damping valve including: ahousing; a first flow-through channel disposed between two pressuremedium connections; a counter-contour; and a flat spring elementconfigured to vary a cross-section of the first flow-through channel;wherein the spring element includes at least one central bore hole, afirst one of an inner contour and an outer contour of the spring elementaxially movable inwardly in accordance with a first direction of flow, asecond one of the inner contour and the outer contour of the springelement axially movable outwardly in accordance with a second directionof flow opposite the first direction of flow, the counter-contourincluding at least one bypass bore hole configured to permit thepressure medium to bypass the spring element, the at least one bypassbore hole providing a second flow-through channel between the twopressure medium connections; the method comprising the step ofintegrating the damping valve in a pressure line of the steering system,the steering system including a steering gear, a hydraulic servo motorconfigured to support a steering torque introduced in the steering gear,two working chambers separated by a piston, a control valve configuredto control a pressure medium delivered by a pressure source to and fromthe two working chambers of the servo motor, the control valve beingconnected to the working chambers via operating lines.
 12. The methodaccording to claim 11, further comprising the step of arranging thedamping valve in a cylinder connection of the control valve.
 13. Themethod according to claim 11, further comprising the step of arrangingthe damping valve in a connection piece on a cylinder of the servomotor.
 14. The method according to claim 11, further comprising the steparranging the damping valve in the operating line.